Definition and Overview
An amniotomy is a procedure performed to release fluid from the amniotic sac to induce labor during childbirth. It is also performed when certain pregnancy-related conditions require the placement of internal monitors such as fetal scalp electrodes and uterine pressure catheters. The procedure is usually performed in a labor or delivery room wherein the obstetrician punctures the amniotic membrane using special surgical tools.
Who Should Undergo and Expected Results
Pregnant women should are advised to under an amniotomy in the following conditions:
- If labor needs to be induced, usually in conjunction with other labor induction methods such as oxytocin infusion
- If there is reason to conduct internal fetal or uterine monitoring to ensure the health and safety of the fetus during labor or childbirth
If labor needs to be augmented, with the procedure helping increase the patient’s plasma prostaglandins
There are many reasons when labor induction may be deemed necessary, such as when:
Fetal distress is detected
- There are maternal stressors involved
- The pregnant patient is way past her due date
If it is not known whether the amniotic sac is still intact prior to labor induction, the doctor can first perform Nitrazine testing, wherein the pH level of the vaginal fluid is tested. If the pH level is between 7 and 7.5, it may indicate the presence of amniotic fluid, which may be a sign that the sac has ruptured.
However, there are conditions wherein an amniotomy or other methods of labor induction is not advised, such as:
- When the patient suffers from or is suspected of having placental previa
- When there is a classical uterine incision
- When the fetus’ positioning is abnormal
- When the patient has an active genital herpes infection
- When there is a known cephalopelvic disproportion
The use of amniotomy is also surrounded by some controversy regarding its effectiveness in inducing labor, with some studies showing only a 30 to 40-minute reduction in total labor time following the procedure.
After an amniotomy, the patient is expected to give birth within 24 hours. If not, there is an increased risk of intrauterine infection, and this may pose severe harm to the fetus even when antibiotics are administered. If birth does not occur within the allotted time, the doctor will recommend either a controlled amniotomy or a caesarean section.
How Does the Procedure Work?
An amniotomy is performed by an obstetrician in a labor or delivery room, with the patient lying on a hospital bed. In some cases, the patient is asked to stay in a semi-sitting position to minimize cord compression and ensure good oxygen supply for the fetus.
The procedure is done using either an amniotic membrane perforator, also known as an amniotomy hook or AmniHook, or an amniotic finger cot, known by the brand names Amnicot and AROM-Cot. The obstetrician will also use a vaginal speculum, or a spinal needle if the patient’s condition or other circumstances require a controlled amniotomy.
Before performing the procedure, certain steps have to be performed to prepare the patient. First, it is crucial to determine the fetus’ presentation and location. Second, the pregnant patient may need to be placed on electronic fetal monitor.
It is also important that the fetal head applies a sufficient amount of pressure on the cervix for the procedure to be effective. If conditions demand an amniotomy but the presenting fetal part is not yet engaged properly, the doctor’s assistant may apply external pressure on the fundal or suprapubic to hold the fetus in the right presenting position as the amniotomy is performed.
When the patient has been prepped for the procedure, the obstetrician proceeds to dilate the cervix in a process similar to that used when performing an internal cervical examination. The doctor then ruptures the amniotic membrane using the hook, timing it in between contractions. As the amniotic fluid begins to flow out, the doctor keeps one hand in the vagina to let it flow in a gradual manner and prevent umbilical cord prolapse. As a follow-up step, the doctor measures and notes the color and consistency of the fluid that comes out.
After an amniotomy, the fetus’ heartbeat will be assessed for one full minute, which is also performed prior to the procedure. This is to check for any changes in the fetus’ condition and any warning signs that may signal fetal distress.
Possible Risks and Complications
There are certain complications associated with an amniotomy. These include:
- Cord prolapse – This commonly occurs as a consequence of the sudden and rapid flow of amniotic fluid, which is why the doctor has to control the flow once the sac has been ruptured.
- Ruptured vasa previa – If this occurs, the patient will have to undergo an emergency caesarean section.
- Cord compression - This refers to a condition wherein the baby’s umbilical cord becomes compressed or flattened, usually as a result of the movement of amniotic fluid as it is released. When this occurs, the fetus may not get enough oxygen and blood, and this in turn places him at risk of heart problems and birth injuries. If mild cord compression is suspected, the patient may simply be given additional oxygen or asked to change position to relieve the compression. However, if these do not work and the fetal heart rate changes drastically, the patient will undergo an emergency caesarean section.
- Fetal blood loss – This can be a life-threatening complication, one that warrants an emergency caesarean section to save the fetus.
- Infection – The pregnant patient may need to be given antibiotics preemptively after an amniotomy is performed. This is because once the amniotic fluid is released, there is a high risk of intrauterine infection.
- Fetal scalp trauma – If the head of the fetus is positioned too closely to the amniotic membrane, it may be possible for some scalp trauma to occur, but this is often very mild.
Chorioamnionitis – This is associated with prolonged membrane rupture.
Cunningham, Levano, Bloom, Hauth, Rouse, Spong. Abnormalities of the Placenta, Umbilical Cord and Membranes. Williams Obstetrics. 23rd. United States: McGraw-Hill; 2010. Chapter 27.
Nachum Z, Garmi G, Kadan Y, Zafran N, Shalev E, Salim R. Comparison between amniotomy, oxytocin or both for augmentation of labor in prolonged latent phase: a randomized controlled trial. Reprod Biol Endocrinol. 2010. 8:136.